NCERT Class 10 Science Chapter 1: Chemical Reactions and Equations Solutions | Assam Eduverse

Chapter Overview

Assam Eduverse presents detailed and student-friendly NCERT Solutions for Class 10 as per CBSE curriculum Science Chapter 1 – Chemical Reactions and Equations. These solutions cover all intext and exercise questions with step-by-step explanations. Students can use these expert-curated answers to boost exam scores and understand key Chemistry concepts. This chapter explores chemical reactions, how they are represented, the types of chemical reactions (combination, decomposition, displacement, double displacement, redox), and the role of oxidation and reduction in daily life.

Chapter 1 also teaches how to write balanced chemical equations and explains the effects of chemical changes. The following sections include intext questions (with page numbers), exercise questions from the textbook, and multiple-choice questions (MCQs) with answers and explanations.

NCERT Solutions for Class 10 Science Chapter 1 Intext Questions

Page 6

Q1. Why should a magnesium ribbon be cleaned before burning in air?

Answer: Magnesium gets covered with a layer of magnesium oxide when exposed to air for long periods. This layer prevents the magnesium from burning efficiently. Hence, it must be cleaned before burning.

Q2. Write the balanced equation for the following chemical reactions.
(i) Hydrogen + Chlorine → Hydrogen chloride
(ii) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
(iii) Sodium + Water → Sodium hydroxide + Hydrogen

Answer:
(i) H₂ + Cl₂ → 2HCl
(ii) 3BaCl₂ + Al₂(SO₄)₃ → 3BaSO₄ + 2AlCl₃
(iii) 2Na + 2H₂O → 2NaOH + H₂

Q3. Why is it important to balance a chemical equation?

Answer: A balanced chemical equation ensures the law of conservation of mass is followed. The number of atoms for each element remains the same on both sides of the reaction. It also helps in determining correct quantities of reactants and products involved.

Page 10

Q1. Write a balanced chemical equation with state symbols for the following reaction:
Barium chloride solution reacts with sodium sulphate solution to give insoluble barium sulphate and sodium chloride solution.

Answer:
BaCl₂ (aq) + Na₂SO₄ (aq) → BaSO₄ (s) + 2NaCl (aq)

This is a double displacement reaction and a precipitation reaction since BaSO₄ is insoluble.

Q2. Why is the amount of gas collected in one of the test tubes in Activity 1.7 (Electrolysis of Water) double the amount collected in the other? Name the gas.

Answer: Water decomposes into hydrogen and oxygen in the ratio 2:1. The chemical equation is:
2H₂O → 2H₂ + O₂
This means the amount of hydrogen gas collected is double that of oxygen.

Page 13

Q1. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?

Answer: Iron is more reactive than copper and displaces copper from copper sulphate solution. This forms greenish iron sulphate and brown copper metal gets deposited.
Equation: Fe + CuSO₄ → FeSO₄ + Cu

Q2. Give an example of a double displacement reaction other than the one given in the book.

Answer: Na₂CO₃ + CaCl₂ → CaCO₃ + 2NaCl
Here, two compounds exchange ions and a white precipitate of calcium carbonate forms.

Q3. Identify the substances oxidised and reduced in the following reactions:
(i) 4Na + O₂ → 2Na₂O
(ii) CuO + H₂ → Cu + H₂O

Answer:
(i) Sodium (Na) is oxidised; Oxygen (O₂) is reduced.
(ii) Hydrogen (H₂) is oxidised; Copper oxide (CuO) is reduced.

NCERT Solutions for Class 10 Science Chapter 1 Textbook Chapter End Questions

Q1. Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) → 2Pb(s) + CO₂(g)

(a) Lead is getting reduced.
(b) Carbon dioxide is getting oxidised.
(c) Carbon is getting oxidised.
(d) Lead oxide is getting reduced.

Correct Answer: (i) (a) and (b)

Explanation: Lead is actually getting reduced and carbon is getting oxidised. So, statement (a) is correct, but (b) is incorrect because CO₂ is not getting oxidised, it is a product of oxidation.

Q2. Fe₂O₃ + 2Al → Al₂O₃ + 2Fe

The above reaction is an example of a:

Correct Answer: (d) displacement reaction

Explanation: Aluminium displaces iron from its oxide, hence it is a displacement reaction.

Q3 What happens when dilute hydrochloric acid is added to iron fillings?

Correct Answer: (a) Hydrogen gas and iron chloride are produced.

Reaction: Fe(s) + 2HCl(aq) → FeCl₂(aq) + H₂(g)

Q4. What is a balanced chemical equation? Why should chemical equations be balanced?

Answer: A balanced chemical equation has equal numbers of atoms of each element on both sides of the equation. It should be balanced to obey the Law of Conservation of Mass, which states that matter can neither be created nor destroyed in a chemical reaction.

Q5.Translate the following statements into chemical equations and then balance them.

(a) N₂ + 3H₂ → 2NH₃
(b) 2H₂S + 3O₂ → 2H₂O + 2SO₂
(c) 3BaCl₂ + Al₂(SO₄)₃ → 2AlCl₃ + 3BaSO₄
(d) 2K + 2H₂O → 2KOH + H₂

Q6. Balance the following chemical equations.

(a) 2HNO₃ + Ca(OH)₂ → Ca(NO₃)₂ + 2H₂O
(b) 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O
(c) NaCl + AgNO₃ → AgCl + NaNO₃
(d) BaCl₂ + H₂SO₄ → BaSO₄ + 2HCl

Q7. Write the balanced chemical equations for the following reactions.

(a) Ca(OH)₂ + CO₂ → CaCO₃ + H₂O
(b) Zn + 2AgNO₃ → Zn(NO₃)₂ + 2Ag
(c) 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu
(d) BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl

Q8. Write the balanced chemical equation for the following and identify the type of reaction in each case.

(a) 2KBr(aq) + BaI₂(aq) → 2KI(aq) + BaBr₂(s) [Double displacement reaction]
(b) ZnCO₃(s) → ZnO(s) + CO₂(g) [Decomposition reaction]
(c) H₂(g) + Cl₂(g) → 2HCl(g) [Combination reaction]
(d) Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) [Displacement reaction]

Q9. What does one mean by exothermic and endothermic reactions? Give examples.

Answer: Exothermic reactions release heat. For example: C(s) + O₂(g) → CO₂(g) + heat. Endothermic reactions absorb heat. For example: Ba(OH)₂ + NH₄Cl → BaCl₂ + NH₃ + H₂O (absorbs heat).

Q10. Why is respiration considered an exothermic reaction? Explain.

Answer: Respiration is the process by which glucose (C₆H₁₂O₆) is broken down in the presence of oxygen to release energy. The reaction is:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

This reaction releases heat, hence it is exothermic.

Q11. Why are decomposition reactions called the opposite of combination reactions? Write equations.

Answer: In decomposition reactions, a compound breaks down into simpler substances. In contrast, in combination reactions, simpler substances combine to form a compound.
Combination: 2H₂ + O₂ → 2H₂O
Decomposition: 2H₂O → 2H₂ + O₂

Q12. Write one equation each for decomposition reactions using (a) heat, (b) light, (c) electricity.

Answer:
(a) CaCO₃ → CaO + CO₂ (heat)
(b) 2AgCl → 2Ag + Cl₂ (light)
(c) 2H₂O → 2H₂ + O₂ (electricity)

Q13. What is the difference between displacement and double displacement reactions? Write equations.

Answer:
Displacement: One element replaces another in a compound. E.g., Zn + CuSO₄ → ZnSO₄ + Cu
Double Displacement: Two compounds exchange ions. E.g., AgNO₃ + NaCl → AgCl + NaNO₃

Q14. In the refining of silver, the recovery of silver from AgNO₃ is done by displacement with copper. Write the equation.

Answer: Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag

Q15. What do you mean by precipitation reaction? Give one example.

Answer: A precipitation reaction results in the formation of an insoluble product. E.g., BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl

Q16. Explain oxidation and reduction with examples.

Answer:
Oxidation: Gain of oxygen or loss of hydrogen. E.g., C + O₂ → CO₂
Reduction: Gain of hydrogen or loss of oxygen. E.g., CuO + H₂ → Cu + H₂O

Q17. A shiny brown substance on heating in air becomes black. Name the substance and black product.

Answer: Shiny brown substance: Copper (Cu), Black product: Copper oxide (CuO)
Reaction: 2Cu + O₂ → 2CuO

Q18. Why do oil and fat-containing food items become rancid?

Answer: They react with oxygen and undergo oxidation, developing unpleasant smell and taste. This process is called rancidity.

Q19. Explain the use of antioxidants in food.

Answer: Antioxidants prevent oxidation, thereby protecting food from becoming rancid. Common antioxidants include BHA and BHT used in snacks.

Q20. What is the significance of a balanced chemical equation?

Answer: It ensures the law of conservation of mass is followed and helps in correct calculation of reactants and products involved in the reaction.

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